1. Field of the Invention
This invention to a method for the manufacture of boron-containing films.
2. Description of the Related Art
In the manufacture of semiconductor devices, CVD (Chemical Vapor Deposition) and epitaxial techniques are used to form a thin film on substrates which include semiconductor wafers.
By the use of these techniques, a boron-containing film for example, such as a BPSG film or a BSG film, is grown on the substrates such as semiconductor wafers. For this purpose, conventionally, diborane (B.sub.2 H.sub.6) is used as a boron source gas and a boron-containing film is formed by the atmospheric pressure CVD process.
Compared with the atmospheric pressure CVD process, the low pressure CVD process, though slower in film forming speed, enables a good-quality film with less pinholes to be formed. When the low pressure CVD systems slow in film formation are used, batch processing which treats several tens to hundreds of wafers at a time is most prevalent. In the low pressure CVD systems, the hot-wall heating system for heating the whole reaction furnace is the dominant heating system, In some cases, it is desirable to form a boron-containing film by the low pressure CVD process described above.
In the conventional method for forming a boron-containing film, however, diborane having a low decomposition temperature is used as a boron source gas. Therefore, when a film is formed by a low pressure CVD process of the hot wall type, diborane decomposes into boron and hydrogen the moment it enters the reaction furnace. As a result, boron is unable to be introduced into the film and a desired film cannot be obtained. Diborane is liable to decompose and decomposes while in storage. Thus, it is difficult to control its concentration and maintain the boron concentration of a film to be formed to a desired value.
Use of boron trichloride as a boron source gas is under consideration. However, the hygroscopicity of boron trichloride makes it difficult to form a film of good quality, Another problem with boron trichloride is its high toxicity, which makes its handling obviously dangerous.